As an example, let’s suppose that stock XYZ is trading at £45 in May. A June 50 call option on the same stock is selling for £5, which is the premium. A June 50 call simply means that the option is a call option, with a £50 strike price that expires in June.
For the purpose of this example, let’s assume that the implied volatility is 14%, and the vega of the option is 0.15. If the implied volatility increased to 15%, then the price of the June 50 call option would increase to £5.15 (£5 + 0.15).
If the implied volatility had instead decreased to 13%, then the price of the option would decline to £4.85 (£5 – 0.15).